Position indicator, position detecting device, position detecting circuit, and position detecting method

ABSTRACT

A signal transmission method is provided, which may be implemented by a position indicator. The signal transmission method includes a step of dividing first information, which is represented in a digital signal of a first defined number of bits, into a plurality of information parts respectively represented in digital signals of a second defined number of bits smaller than the first defined number of bits. The signal transmission method includes a step of transmitting, from the position indicator to a position detecting device, the information parts, and distinguishing information usable for distinguishing the information parts from each other, wherein each of the information parts is transmitted with second information different from the first information.

BACKGROUND Technical Field

The present disclosure relates to a position indicator, and moreparticularly to a position indicator that transmits large-sizeinformation to a position detecting device. The present disclosure alsorelates to a position detecting device configured to detect the positionof such a position indicator, a position detecting circuit for use bythe position detecting device, and a position detecting method fordetecting the position of such a position indicator.

Description of the Related Art

There exist touch-sensitive input systems configured to include aposition detecting device that is a plate-like input unit, and aposition indicator such as an electronic pen or a cursor. On someposition detecting devices, a simple rod or a human fingertip may beused as the position indicator. Such input systems are usually calledtablets or digitizers. They are utilized extensively for inputting textsand illustrations to computers such as personal computers and tabletterminals.

The position detecting device has a plurality of linear conductors(e.g., loop coils) arranged in a matrix pattern. The position detectingdevice is configured to detect the position of the position indicator onthe basis of voltages or their variations generated by the linearconductors being approached by the position indicator.

Various specific schemes for position detection include the capacitancesystem and the electromagnetic induction system. The capacitance systeminvolves using capacitance generated between the position indicator andlinear conductors. The capacitance system may be further classified intothe self-capacitance system that detects the change in voltage on eachlinear conductor, and the mutual capacitance system that detects thechange in potential difference between the linear conductorsintersecting with each other. The self-capacitance system may be stillfurther classified into a system in which the position detecting deviceimpresses a voltage to the linear conductors, and another system inwhich the position indicator transmits a signal to the linear conductorscausing them to generate voltages. The former system may be employedwhere the position indicator cannot transit a signal as when thefingertip is used as the position indicator. The latter system may beutilized where the position indicator can transmit a signal. Meanwhile,the electromagnetic induction system is a system in which the positiondetecting device uses the linear conductors as a transmission antenna totransmit electromagnetic waves to the position indicator which in turntransmits a signal for detection by the position detecting device usingthe linear conductors as a receiving antenna. With the electromagneticinduction system, the transmission and the reception are performed on atime-sharing basis.

The detection of the position by the position detecting device isexplained below using an example of the self-capacitance system in whichthe position indicator transmits a signal. With this system, theposition detecting device detects the position while the positionindicator keeps transmitting a determined continuous signal. During thetransmission of the continuous signal by the position indicator, thelinear conductors individually generate higher voltages the shortertheir distance to the position indicator. The position detecting deviceindividually scans a plurality of linear conductors for levels(voltages) to detect the linear conductor bearing the highest voltageamong the conductors arranged in the X direction and the linearconductor carrying the highest voltage among the conductors arranged inthe Y direction perpendicular to the X direction. The voltages of thetwo detected linear conductors and the voltages of nearby linearconductors are substituted in a determined mathematical formula, and theresult calculated by the formula is acquired as the position of theposition indicator. This calculating method allows the position of theposition indicator to be detected with a resolution finer than the pitchat which the linear conductors are arranged.

Meanwhile, some of the position indicators capable of transmittingsignals are configured to transmit not only the above-mentionedcontinuous signal but also various items of information. Specificexamples of the information to be transmitted include writing pressureinformation, on-off information (side switch information) about switchestypically provided on the side surface or the like of the positionindicator, and an identifier (ID) unique to each position indicator.Patent Document 1 discloses a typical position detector that transmitssuch items of information to a position detecting device.

The transmitting of the diverse items of information from the positionindicator and the transmitting of the continuous signal therefrom areperformed on a time-sharing basis. An example disclosed in PatentDocument 1 is cited here to give a specific description of the two kindsof transmitting on a time-sharing basis. The position indicator firsttransmits the continuous signal. During the continuous signaltransmission, the position detecting device detects the position of theposition indicator. Within a determined time of the completion of thecontinuous signal transmission, the position detecting device transmitsa determined control signal (command) to the position indicator. Uponreceipt of the control signal, the position indicator transmitsinformation corresponding to the content of the control signal to theposition detecting device. Although not described in Patent Document 1,there are cases where the position indicator transmits various items ofinformation regardless of the control signal from the position detectingdevice.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Laid-open No. 2011-086253

BRIEF SUMMARY

Technical Problem

In recent years, the size of the information (bit count) transmittedfrom the position indicator to the position detecting device hasincreased considerably. For example, the ID unique to each positionindicator includes such diverse items of information as the individualnumber, owner identification code, device type, and manufacturer numberof the position indicator. The information, if it includes check bits,can amount to not less than 60 bits.

As described above, the transmitting of diverse items of informationfrom the position indicator and the transmitting of the above-mentionedcontinuous signal for position detection are performed on a time-sharingbasis. It follows that with a growing size of the transmittedinformation entailing a longer transmission time, the number of timesthe continuous signal is sent per unit time decreases. This means thatthere is a trade-off relation between the sampling rate of the positioninformation and the amount of the information transmitted. Anexcessively large size of the transmission information may make itimpossible for the operation of position detection to follow the rapidmovement of the position indicator. For this reason, the existing inputsystems can transmit only up to a certain size of information from theposition indicator to the position detecting device.

An embodiment facilitates a position indicator transmitting large-sizeinformation to a position detecting device without reducing the samplingrate of position information.

Technical Solution

According to an embodiment, there is provided a position indicator thattransmits to a position detecting device a plurality of signal blockssuccessively, each of the signal blocks including a continuous signalfor position detection and a first modulated signal acquired bymodulating one of a plurality of divided information parts constitutingfirst information. The position indicator transmits the entire firstinformation by transmitting the plurality of signal blocks.

According to an embodiment, there is provided a position detectingdevice that receives from a position indicator a plurality of signalblocks successively, each of the signal blocks including a continuoussignal for position detection and a first modulated signal acquired bymodulating one of a plurality of divided information parts constitutingfirst information. The position detecting device detects positioninformation indicating the position of the position indicator from eachof the signal blocks on the basis of the continuous signal, and acquiresthe first information on the basis of the first modulated signalincluded in each of the plurality of signal blocks.

According to an embodiment, there is provided a position detectingcircuit connected to receiving circuitry. The position detecting circuitreceives a plurality of signal blocks successively from a positionindicator via the receiving circuitry, each of the signal blocksincluding a continuous signal for position detection and a firstmodulated signal acquired by modulating one of a plurality of dividedinformation parts constituting first information. The position detectingcircuit detects position information indicating the position of theposition indicator from each of the signal blocks on the basis of thecontinuous signal, and acquires the first information on the basis ofthe first modulated signal included in each of the plurality of signalblocks.

According to an embodiment, there is provided a position detectingmethod including: a transmitting step of transmitting a plurality ofsignal blocks successively from a position indicator to a positiondetecting circuit, each of the signal blocks including a continuoussignal for position detection and a first modulated signal acquired bymodulating one of a plurality of divided information parts constitutingfirst information; and a receiving step of receiving the plurality ofsignal blocks successively to detect position information indicating theposition of the position indicator from each of the signal blocks on thebasis of the continuous signal, while acquiring the first information onthe basis of the first modulated signal included in each of theplurality of signal blocks.

Advantageous Effect

In an embodiment, the first information is divided into a plurality ofsignal blocks each including a continuous signal for position detection,before the signal blocks are transmitted. This facilitates the positionindicator transmitting large-size information to the position detectingdevice without reducing the sampling rate of the position information.

In an embodiment, a position indicator comprises a housing; andcircuitry, which, in operation, transmits a plurality of signal blockssuccessively to a position detecting device, each of the signal blocksincluding: a position detection signal; a first modulated signalacquired by modulating one part of a plurality of divided parts ofposition indicator identification information; and a second modulatedsignal acquired by modulating current position indicator statusinformation acquired successively from a signal supplied to a controlterminal or from a voltage state of the control terminal, wherein theposition indicator transmits the plurality of divided parts of positionindicator identification information by transmitting the plurality ofsignal blocks. In an embodiment, the first modulated signal includesinformation indicative of a position of the one of the plurality ofdivided parts in the position indicator identification information. Inan embodiment, the first modulated signal includes an error-detectingcode to detect an error in the one of the plurality of divided parts ofthe position indicator identification information. In an embodiment,each bit of the first and second modulated signals is transmitted in aclock cycle during which a signal level of the bit is at a first levelfor at least a portion of the clock cycle; and a signal level of theposition detection signal remains at a second level different from thefirst level over a time period longer than the clock cycle. In anembodiment, a number of the plurality of divided parts of positionindicator identification information is three. In an embodiment, theposition indicator status information includes writing pressureinformation indicating a pressure sensed by the position indicator, andat least one of: side switch information indicating an on-off state of aswitch provided on the position indicator; charging request informationindicating whether the position indicator needs to be charged; tiltinformation indicating a tilt angle of the position indicator relativeto the position detecting device; and rotation information acquired by arotation sensor incorporated in the position indicator. In anembodiment, the position indicator comprises: a core body, which, inoperation, contacts the position detecting device, wherein the writingpressure information is information acquired by detecting pressureapplied to the core body while the position detection signal is in anactive state.

In an embodiment, a position detecting device comprises: a sensor; andsignal processing circuitry coupled to the sensor, wherein the signalprocessing circuitry, in operation, receives from a position indicator aplurality of signal blocks successively, each of the signal blocksincluding: a position detection signal; a first modulated signalacquired by modulating one part of a plurality of divided parts ofposition indicator identification information; and a second modulatedsignal acquired by modulating current position indicator statusinformation acquired successively; and detects position informationindicating the position of the position indicator from each of thesignal blocks based on the position detection signal, acquires thecurrent position indicator status information based on the secondmodulated signal, and acquires the one part of the position indicatoridentification information based on the first modulated signal. In anembodiment, the signal processing circuitry, in operation, acquires theplurality of divided parts of the position indicator identificationinformation by receiving the plurality of signal blocks. In anembodiment, when the signal processing circuitry detects an error inacquisition of position indicator identification information, the signalprocessing circuitry continues to detect position information indicatingthe position of the position indicator based on the position detectionsignal and to acquire current position indicator status informationbased on the second modulated signal. In an embodiment, the firstmodulated signal includes information indicative of a position of theone of the plurality of divided parts in the position indicatoridentification information; and the signal processing circuitry, inoperation, acquires the position indicator identification information bycombining the respective parts included in each of the plurality ofsignal blocks based on the information indicative of the position of therespective parts included in each of the plurality of signal blocks. Inan embodiment, the first modulated signal includes an error-detectingcode to detect an error in the one part of the plurality of dividedparts of the position indicator identification information; and for eachof the signal blocks, the signal processing circuitry, in operation,determines whether the part of the position indicator identificationinformation included in the first modulated signal associated with thesignal block is accurate based on the error-detecting code included inthe first modulated signal. In an embodiment, the signal processingcircuitry, from a time when the plurality of signal blocks start beingreceived until reception thereof is completed, retains a plurality ofpieces of the position information acquired from the position detectionsignal included in each of the plurality of signal blocks, and aplurality of pieces of the current position indicator status informationacquired from the second modulated signal included in each of theplurality of signal blocks. In an embodiment, when the signal processingcircuitry successfully acquires the position indicator identificationinformation from the plurality of signal blocks, the signal processingcircuitry associates the retained pieces of the position information andthe retained pieces of the current position indicator status informationwith the acquired position indicator identification information. In anembodiment, the signal processing circuitry, in operation, is coupled toa processor; and while the position indicator identification informationis being acquired, the signal processing circuitry outputs to theprocessor each of the retained pieces of the position information andeach of the retained pieces of the current position indicator statusinformation. In an embodiment, the signal processing circuitry, inoperation, is coupled to a processor; and the signal processingcircuitry, in operation, associates the retained pieces of the positioninformation and the retained pieces of the current position indicatorstatus information with the acquired position indicator identificationinformation before outputting the associated information to theprocessor.

In an embodiment, a system, comprises: receiving circuitry, which, inoperation, receives a plurality of signal blocks successively from aposition indicator, each of the signal blocks including: a positiondetection signal; a first modulated signal acquired by modulating onepart of a plurality of divided parts of position indicatoridentification information; and a second modulated signal acquired bymodulating current position indicator status information acquired; andposition detecting circuitry, coupled to the receiving circuitry,wherein the position detecting circuitry detects position informationindicating the position of the position indicator from each of thesignal blocks based on the position detection signal, acquires thecurrent position indicator status information based on the secondmodulated signal, and acquires the one part of the plurality of dividedparts of the position indicator identification information based on thefirst modulated signal included in each of the plurality of signalblocks. In an embodiment, the first modulated signal includesinformation indicative of a position of the one of the plurality ofdivided parts in the position indicator identification information; andthe position detecting circuitry, in operation, acquires the positionindicator identification information by combining the respective partsincluded in each of the plurality of signal blocks based on theinformation indicative of the position of the respective part includedin each of the plurality of signal blocks. In an embodiment, the firstmodulated signal includes an error-detecting code to detect an error inthe one part of the plurality of divided parts of the position indicatoridentification information; and for each of the signal blocks, theposition detecting circuitry, in operation, determines whether the partof the position indicator identification information included in thefirst modulated signal associated with the signal block is accuratebased on the error-detecting code included in the first modulatedsignal. In an embodiment, from a time when the plurality of signalblocks start being received until reception thereof is completed, theposition detecting circuitry, in operation, stores a plurality of piecesof the position information acquired from the position detection signalincluded in each of the plurality of signal blocks and a plurality ofpieces of the current position indicator status information acquiredfrom the second modulated signal included in each of the plurality ofsignal blocks in a storage circuit. In an embodiment, when the positiondetecting circuitry successfully acquires the position indicatoridentification information from the plurality of signal blocks, theposition detecting circuitry associates the stored pieces of theposition information in the storage circuit and the stored pieces of thecurrent position indicator status information in the storage circuitwith the acquired position indicator identification information. In anembodiment, the system comprises: a processor coupled to the positiondetecting circuitry, wherein the position detecting circuitry associatesthe stored pieces of the position information in the storage circuit andthe stored pieces of the current position indicator status informationin the storage circuit with the acquired position indicatoridentification information before outputting the associated informationto the processor.

In an embodiment, a method comprises: transmitting a plurality of signalblocks successively from a position indicator to a position detectingcircuit, each of the plurality of signal blocks including: a positiondetection signal for position detection; a first modulated signalacquired by modulating one part of a plurality of divided parts ofposition indicator identification information; and a second modulatedsignal acquired by modulating current position indicator statusinformation acquired successively from a signal supplied to a controlterminal or from a voltage state of the control terminal; receiving theplurality of signal blocks successively; detecting position informationindicating the position of the position indicator from each of thereceived signal blocks based on the position detection signal; acquiringthe current position indicator status information based on the secondmodulated signal from each of the signal blocks; and acquiring theplurality of divided parts of the position indicator identificationinformation based on the first modulated signal included in each of theplurality of signal blocks.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a system configuration of atouch-sensitive input system 1 and functional blocks of a tablet 10attached to the input system 1 of an embodiment.

FIG. 2A is a circuit diagram illustrating examples of an internalcircuit of an electronic pen 20 indicated in FIG. 1 and FIG. 2B is aschematic block diagram illustrating functional blocks of a controller40 indicated in FIG. 2A.

FIG. 3A is a timing chart illustrating various examples of signalsrelated to the electronic pen 20 indicated in FIG. 2A and FIG. 3B is atiming chart illustrating various signals related to the tablet 10indicated in FIG. 1 .

FIG. 4A is a schematic view illustrating an example structure of aunique ID stored in a unique ID storage section 40 a indicated in FIG.2B and FIG. 4B is a schematic view illustrating an example structure ofa transmission information block TIB generated by an oscillation controlsection 40 c indicated in FIG. 2B.

FIG. 5 is a schematic view illustrating the sequence in which aplurality of transmission information blocks TIB generated by theoscillation control section 40 c indicated in FIG. 2B are transmitted inan embodiment.

FIGS. 6A and 6B are explanatory views of example processing performed bythe tablet 10 indicated in FIG. 1 .

FIG. 7 is a circuit diagram illustrating an internal circuit of avariation of the electronic pen 20 according to an embodiment.

DETAILED DESCRIPTION

Embodiments are described below in detail with reference to theaccompanying drawings.

A touch-sensitive input system 1 of an embodiment is configured toinclude a tablet 10 (position detecting device) having a plurality ofelectrodes (linear conductors) 11X and 11Y arranged in a matrix pattern,an electronic pen 20 (position indicator) designed to transmit a signal,and a computer 30 (processor) coupled to the tablet 10, as illustratedin FIG. 1 .

The input system 1 is of the self-capacitance type. The tablet 10 isconfigured to detect the position of the electronic pen 20 on the basisof voltages generated by the electrodes 11X and 11Y receiving the signaltransmitted from the electronic pen 20. In the ensuing paragraphs, thestructure of the tablet 10 and that of the electronic pen 20 will bedescribed first, followed by a description of the electronic pen 20 inoperation and a description of the tablet 10 in operation, in thatorder.

As illustrated in FIG. 1 , the tablet 10 is configured to include atablet sensor 11, a selection circuit 12, an amplifier circuit 13, aband-pass filter 14, a detector circuit 15, a sample hold circuit 16, ananalog-to-digital converter circuit 17, and a microprocessor 18(position detecting circuit). Of these components, the tablet sensor 11,selection circuit 12, amplifier circuit 13, band-pass filter 14,detector circuit 15, sample hold circuit 16, and analog-to-digitalconverter circuit 17 function as the receiving circuitry for receivingsignals from the electronic pen 20.

The tablet sensor 11 is configured to have a transparent glasssubstrate, not illustrated. The plurality of electrodes 11X extend inthe X direction over the substrate surface (the face close to theelectronic pen 20) and are arranged an equal distance apart from eachother in the Y direction perpendicular to the X direction. The pluralityof electrodes 11Y extend in the Y direction over the back side of thesubstrate (the face away from the electronic pen 20) and are arranged anequal distance apart from each other in the X direction. The electrodes11X and 11Y are transparent conductors. The electrodes may be formed ofindium tin oxide (ITO), for example. In an embodiment, as many as 30electrodes 11X and 40 electrodes 11Y may be provided.

The tablet sensor 11 is disposed on a display device, not illustrated.Since the tablet sensor 11 is formed of the above-mentioned transparentmembers, an image displayed on the display device is transmitted throughthe tablet sensor 11 and is visible by the user of the input system 1.In this manner, the input system 1 allows the user to experience writingwith the electronic pen 20 on the image displayed on the display device.

From an opposite point of view, it is because the tablet sensor 11 isdisposed on the display device that the tablet sensor 11 is formed ofthe transparent members. An embodiment may also be applied to tabletsthat have no display area. In this case, the tablet sensor 11 need notbe formed of transparent members. That means the tablet sensor 11 maycomprise, for example, copper wires instead of ITO.

The selection circuit 12 selects one of the electrodes 11X and 11Y andcouples the selected electrode to the amplifier circuit 13. Theamplifier circuit 13 is supplied with the voltage of the electrodeselected by the selection circuit 12. As will be explained later in moredetail, the electronic pen 20 is configured to amplitude-modulate a sinewave signal of a determined frequency using the transmissioninformation. On each of the electrodes 11X and 11Y develops a voltagesignal reflecting the amplitude of the sine wave signal thustransmitted.

The amplifier circuit 13 amplifies the voltage signal supplied from theselection circuit 12 and outputs an amplified voltage signal to theband-pass filter 14. The band-pass filter 14 extracts only the componentof the above-mentioned determined frequency from the voltage signaloutput from the amplifier circuit 13, and outputs the extractedcomponent to the detector circuit 15. The detector circuit 15 generatesan envelope signal S1 by envelope-detecting the voltage signal outputfrom the band-pass filter 14, and outputs the generated envelope signalS1 to the sample hold circuit 16. The sample hold circuit 16 performsthe sample and the hold operations a determined time apart on theenvelope signal S1 output from the detector circuit 15. Theanalog-to-digital converter circuit 17 generates a digital signal S2 bysubjecting to analog-to-digital conversion the signal being held by thesample hold circuit 16, and outputs the generated digital signal S2 tothe microprocessor 18.

The electronic pen 20 transmits signals through binary amplitude shiftkeying (ASK), as will be described later. The analog-to-digitalconverter circuit 17 assumes that the input signal was modulated throughmulti-value ASK when converting the input signal to the digital signalS2. This process is intended to let the microprocessor 18 acquire anapproximate value of the voltage represented by the voltage signaloutput from the selector circuit 12.

The microprocessor 18 is a processor that incorporates a storage device19 and operates on programs held in the storage device 19. The storagedevice 19 includes a read only memory (ROM) and a random access memory(RAM), for example. The operations performed by the microprocessor 18include controlling the selector circuit 12, sample hold circuit 16, andanalog-to-digital converter circuit 17; and causing the storage device19 temporarily to store the information represented by the digitalsignal S2 supplied from the analog-to-digital converter circuit 17before outputting the information to the computer 30 at a suitabletiming.

As illustrated in FIG. 2A, the electronic pen 20 is configured to have acontroller 40, a voltage converter circuit 41, a diode 42, capacitors 43to 46, a resistive element 47, switches 48 and 49, a vibrator oroscillator 50, a conductor core 51 (core body), a tip conductor 52, anda charging terminal 53.

The controller 40 is a processor that includes a ROM and a RAM. Thecontroller 40 is configured to operate in synchronism with a clocksignal generated by the vibrator 50 and in conformity with thedescription of programs stored in the ROM. The cycle of the clock signalis 60 microseconds for example. In addition to the terminals connectedto the vibrator 50, the controller 40 has a power supply terminal Vcc, aground terminal GND, and control terminals P1 to P6.

The power supply terminal Vcc is connected with the capacitor 43 via thevoltage converter circuit 41. The capacitor 43 is an electric doublelayer capacitor that serves as the power source of the electronic pen20. The capacitor 43 is configured to have its anode connected to theinput terminal of the voltage converter circuit 41, with the cathode ofthe capacitor 43 being grounded. The voltage converter circuit 41 is adirect current-to-direct current (DCDC) converter acting to convert thevoltage across the capacitor 43 to a rated voltage of the controller 40.

Although this embodiment uses an electric double layer capacitor as thepower source, this is not limitative. Alternatively, other powerconfigurations may be employed, such as a primary battery such as alithium battery or a dry cell, or a secondary battery such as anickel-hydrogen storage cell may be used as the power source.

The anode of the capacitor 43 is also connected to the charging terminal53 via the diode 42. The charging terminal 53 is made up of twoterminals: a positive terminal and a negative terminal. The anode of thecapacitor 43 is connected with the positive terminal of the chargingterminal 53. The negative terminal is grounded inside the electronic pen20. The charging terminal 53 is a terminal to which an external powersupply unit is connected. When the external power supply unit isconnected to the charging terminal 53, the capacitor 43 is charged. Inan embodiment, a dedicated battery charger (not illustrated) of theelectronic pen 20 is used as the external power supply unit.

The capacitor 44 is connected interposingly between the power supplyterminal Vcc and the ground terminal GND. The capacitor 44 is providedto stabilize the power supply voltage fed from the voltage convertercircuit 41 to the controller 40. In an embodiment, the capacitor 44 isan aluminum electrolytic capacitor of from tens to hundreds of μF forexample.

The voltage converter circuit 41 is configured to perform eitherstep-down operation or step-up operation in accordance with the voltageacross the capacitor 43. That is, the maximum voltage across thecapacitor 43 is designed to exceed the rated voltage of the controller40. It follows that while the capacitor 43 is being fully charged, thevoltage across the capacitor 43 exceeds the rated voltage of thecontroller 40. In this case, the voltage converter circuit 41 performsstep-down operation to bring the voltage supplied to the power supplyterminal Vcc down to the rated voltage of the controller 40. On theother hand, if the capacitor 43 is insufficiently charged, the voltageacross the capacitor 43 may fall below the rated voltage of thecontroller 40. In this case, the voltage converter circuit 41 performsstep-up operation to bring the voltage supplied to the power supplyterminal Vcc up to the rated voltage of the controller 40.

The voltage converter circuit 41 is also connected to the controlterminals P1 and P2 of the controller 40. When the controller 40supplies a determined control signal to the voltage converter circuit 41via the control terminal P1, the voltage converter circuit 41 detectsthe voltage across the capacitor 43 and outputs to the control terminalP2 a signal representing the detected voltage value. The controller 40is configured, given the signal thus supplied, to determine whether ornot the capacitor 43 needs to be charged.

The input system 1 has the function of notifying the user of aninsufficiently charged state of the capacitor 43. What follows is a morespecific explanation of this function. The controller 40 is configuredto transmit to the tablet 10 a signal representing the result of thedetermination of whether or not the capacitor 43 needs to be charged (aspecific method of transmitting the signal will be discussed later). Thecomputer 30 receives the signal via the tablet 10. If the signalindicates the need to charge the capacitor 43, an indication to thateffect is displayed typically on a display device, not illustrated. Theindication allows the user to know the need for charging the electronicpen 20. Given the indication, the user places the electronic pen 20 onthe above-mentioned battery charger to start charging the capacitor 43.

The control terminal P3 is grounded via the capacitor 45 and theresistive element 47. The capacitor 45 is a variable capacitancecapacitor coupled to the conductor core 51, and is configured to vary incapacitance depending on the pressing force (writing pressure) in effectwhen the electronic pen 20 is pressed against the tablet 10. Thecontroller 40 is configured to acquire the writing pressure from thecapacitance of the capacitor 45, as will be discussed later in moredetail.

The method of detecting the pressing force (writing pressure) is notlimited to the use of a variable capacitance capacitor as describedabove. The electronic pen 20 may be configured to detect the pressingforce (writing pressure) using other methods. For example, analternative method may involve detecting the pressing force in terms ofchanges in inductance of plurality of ferrite cores being moved. Anothermethod may involve using semiconductor devices, namely micro electromechanical systems (MEMS) to detect the pressing force. Still anothermethod may involve optically detecting the pressing force.

The control terminals P4 and P5 are grounded via the switches 48 and 49,respectively. The switches 48 and 49 are disposed on the surface of theelectronic pen 20 (side switches) and are operable by the user. Thecontroller 40 has the function of determining the on-off states of theswitches 48 and 49 from the voltage states of the control terminals P4and P5. Although this embodiment has two switches 48 and 49, there maybe provided no switch, one switch, or three or more switches instead.

The control terminal P6 is coupled to the conductor core 51 via thecapacitor 46. The conductor core 51 is structured to protrude from thetip conductor 52 at the tip of the housing of the electronic pen 20. Thetip conductor 52 is grounded.

The electronic pen 20 has the function of transmitting anamplitude-modulated sine wave signal of a determined frequency, asmentioned above. This sine wave signal is generated by the controller40. The controller 40 is configured to output the sine wave signal fromthe control terminal P6. The sine wave signal thus output is fed to theconductor core 51 via the capacitor 46. Note that the capacitor 46 isprovided to remove the direct-current bias component from the sine wavesignal. The sine wave signal reaching the conductor core 51 is output aselectromagnetic waves and received by the electrodes 11X and 11Y of thetablet 10 as discussed above.

The structure of examples of the tablet 10 and that of the electronicpen 20 were explained above. What follows is an explanation of examplecontent of the information sent from the electronic pen 20 to the tablet10, followed by an explanation of an example transmission operationperformed by the electronic pen 20.

As illustrated in FIG. 2B, the controller 40 of the electronic pen 20 isfunctionally configured to have a unique ID storage section or circuitry40 a, an information acquisition section or circuitry 40 b, anoscillation control section or circuitry 40 c, and an oscillator 40 d.

The unique ID storage section 40 a stores a unique ID given beforehandto the electronic pen 20. The unique ID is information unique to thiselectronic pen 20 and is different from the ID assigned to any otherelectronic pen 20. For example, the unique ID is structured to includeor indicate the individual number of the electronic pen 20, the owneridentification code (e.g., user ID assigned to the electronic pen owner)of the electronic pen 20, and the type and the manufacturer number ofthe electronic pen 20. The unique ID may be 51 bits in size, forexample.

The information acquisition section 40 b is configured to acquire theunique ID from the unique ID storage section 40 a and to also acquireother diverse information from the signals supplied to theabove-mentioned control terminals P2 to P5 or from their voltage states.What follows is an explanation of various examples of items ofinformation that may be acquired by the information acquisition section40 b through the control terminals.

The control terminal P2 is supplied with the signal representing thevoltage across the capacitor 43 as described above. On the basis of thissignal, the information acquisition section 40 b determines whether ornot the capacitor 43 needs to be charged, and generates charging requestinformation indicating the result of the determination. The chargingrequest information is, for example, one-bit information that is 1 whencharging is needed and 0 when charging is not needed.

The information acquisition section 40 b is also configured to acquirewriting pressure information representing the above-mentioned writingpressure from the voltage state of the control terminal P3. FIG. 3Aillustrates example changes in the voltage state of the control terminalP3 in effect when the writing pressure information is acquired. Asillustrated in the figure, the writing pressure information is acquiredwhile a continuous signal CS for position detection is being sent.

More specifically, the information acquisition section 40 b referencesthe potential on the control terminal P3 as the power supply potentialover a determined time period after the electronic pen 20 has started totransmit the continuous signal CS. The power supply potential is 1.5 V,for example. This operation is intended to detect the writing pressurein effect at that point in time. That is, the operation causes thecapacitor 45 to accumulate the charges of which the amount variesdepending on the capacitance of the capacitor 45 in effect at the time.Since the capacitance of the capacitor 45 varies with the writingpressure as described above, the amount of the charges accumulated inthe capacitor 45 reflects the writing pressure.

The information acquisition section 40 b then places the controlterminal P3 in the high-impedance state. This causes the capacitor 45 todischarge the accumulated charges through the resistive element 47. Theinformation acquisition section 40 b measures an elapsed time Tp fromthe time the capacitor 45 starts being discharged until the potential ofthe control terminal P3 reaches 0.75 V, half the power supply potentialof 1.5 V. The larger the capacitance of the capacitor 45, the longer theelapsed time Tp thus measured. The information acquisition section 40 bcan thus acquire the writing pressure information from the measuredelapsed time Tp. The writing pressure information acquired in thismanner is 10 to 12 bits in size.

The information acquisition section 40 b further generates side switchinformation representing the on-off states of the switches 48 and 49from the voltage states of the control terminals P4 and P5. Since thisembodiment has two switches, the side switch information is 2 bits insize.

The information acquisition section 40 b supplies the oscillationcontrol section 40 c with the diverse information thus acquired (e.g.,unique ID, charging request information, writing pressure information,and side switch information). The information acquisition section 40 bmay also acquire information other than the information described aboveand feed such information to the oscillation control section 40 c. Theother information may include tilt information representing the tiltangle of the electronic pen 20 relative to the tablet 10, fingerprintinformation acquired by a fingerprint sensor incorporated in theelectronic pen 20, grip strength information acquired by a pressuresensor incorporated in the electronic pen 20, rotation informationacquired by a rotation sensor incorporated in the electronic pen 20, andpower supply state information indicative of the charged state of thepower source, for example.

The oscillation control section 40 c is a circuit that controls theoscillator 40 d in operation to output to the oscillator 40 d a signalmodulated through binary ASK. The oscillator 40 d is configured togenerate a sine wave signal of a determined frequency and to output thegenerated sine wave signal to the control terminal P6. The output of thesignal from the oscillator 40 d is turned on or off under control of theoscillation control section 40 c on the basis of the diverse informationsupplied from the information acquisition section 40 b, for example. Asa result of this, the signal output from the control terminal P6 ismodulated through binary ASK, as illustrated in FIG. 3A. The oscillator40 d of this embodiment is configured to operate in synchronism with theclock signal generated by the vibrator 50. Alternatively, the oscillator40 d may be configured to oscillate at another frequency withoutsynchronizing with the clock signal. In such a case, the oscillator 40 dmay be disposed outside the controller 40 in a position connected to thecontrol terminal P6.

Although this embodiment utilizes binary ASK, other modulation methodsmay obviously be used instead. For example, another type of amplitudemodulation such as multi-value ASK, frequency shift keying, phase shiftkeying, or quadrature amplitude modulation may be adopted alternatively.

Described below in detail with reference to FIGS. 3A, 4A, 4B and 5 is anexample transmission operation performed by the electronic pen 20 usingthe oscillation control section 40 c and the oscillator 40 d.

The oscillation control section 40 c and the oscillator 40 d areconfigured to transmit signals successively in units of a signal block.FIG. 3A illustrates an example of the signal block. In the example ofFIG. 3A, one signal block is assigned a time period of 5 milliseconds.The first-half time period of 2.2 milliseconds is assigned totransmitting the continuous signal CS for position detection. Theabove-described diverse information is transmitted by use of thesecond-half time period of 2.8 milliseconds.

In the example of FIG. 3A, the position information is detected every 5milliseconds by the tablet 10. If position information detection isperformed at a frequency in this range, the phenomenon of the computer30 being unable to give display fast enough to keep up with the rapidmovement of the electronic pen 20 does not usually happen.

On the other hand, in the example of FIG. 3A, it is impossible totransmit an entire unique ID in a single signal block. That is, theoscillation control section 40 c of this embodiment is configured tooperate at a single rate regarding the clock signal (one cycle Td=60microseconds) generated by the vibrator 50 illustrated in FIG. 2A, aswell as to perform modulation through binary ASK as discussed above.Thus the amount of information that can be transmitted in 2.8milliseconds is merely up to 46 bits (2.8/0.06≈46.7). Considering thetime required to transmit a start signal SS, to be described later, theamount of the information that can be actually sent drops further toapproximately 43 bits. It follows that if the unique ID is 51-bitinformation as mentioned above, the entire unique ID cannot be sent in asingle signal block.

The second-half portion of the signal block is explained morespecifically below. As illustrated in FIG. 3A, the second half of thesignal block includes a start signal SS and a transmission informationblock TIB. The start signal SS is a known signal notifying the tablet 10that the transmission of the continuous signal CS is completed. Thestart signal SS signal is transmitted following the continuous signalCS. The transmission information block TIB is structured with a signalmodulated on the basis of the diverse information acquired by theinformation acquisition section 40 b.

Here, the oscillation control section 40 c provides on-off control ofthe output of the oscillator 40 d based on the transmission informationin synchronism with the rising edges of the clock signal generated bythe vibrator 50 illustrated in FIG. 2A, and turns off the output of theoscillator 40 d in synchronism with the falling edges of the clocksignal. This fixes to 0 the amplitude of the transmitted signal in thesecond half of one clock cycle. As a result, the signal involving thetransmission information block TIB is an intermittent signal that alwaysincludes a low level (first level) period at intervals of one clockcycle as illustrated in FIG. 3B. This structure is adopted so that thecontinuous signal CS for position detection (a signal that remains atthe high level (second level) over a period longer than one clock cycle)and the transmission information block TIB will be clearly distinguishedfrom each other.

The internal structure of the transmission information block TIB isexplained below in more detail. The program that regulates the operationof the oscillation control section 40 c categorizes beforehand each ofthe various items of information acquired by the information acquisitionblock 40 b into one of two types: the type of information that can betransmitted in one transmission information block TIB, and the type ofinformation that cannot be transmitted in one transmission informationblock TIB. The former type of information will be referred to as thesecond information and the latter type of information as the firstinformation hereunder. With this embodiment, the unique ID iscategorized as the first information, and other items of information(charging request information, writing pressure information, and sideswitch information) are categorized as the second information. Of theother items of information mentioned above, e.g., tilt information,fingerprint information, grip strength information, and rotationinformation, the fingerprint information and the grip strengthinformation may be categorized as the first information because of theirrelatively large sizes, and the rotation information may be categorizedas the second information because of its relatively small size. The tiltinformation may be categorized as the first information if its size islarge and as the second information if its size is small.

The oscillation control section 40 c has the function of dividing thefirst information into a plurality of information parts. FIG. 4Aillustrates an example of the unique ID as the first information. Inthis example, the oscillation control section 40 c divides the uniqueID, which is made up of bits D0 to Dx having x+1-bit information, intoas many as n ID blocks (information parts) each having m bits. At thetime of dividing, the oscillation control section 40 c provides eachinformation part with a division number (division information)indicating the position of that information part inside the firstinformation. In the example of FIG. 4A, the oscillation control section40 c provides the ID blocks with block numbers A, B, . . . , n−1, nserving as the division numbers. Where the unique ID is 51 bits in size,the number n may be “3” (the unique ID is divided into three parts each17 bits long). The block numbers A, B, . . . , n−1, n are a-bitinformation each.

The oscillation control section 40 c also has the function of generatingan error-detecting code for the receiving side to detect an error. IDblock check bits, b bits, illustrated in FIG. 4B constitute a typicalerror-detecting code. In an embodiment, the error-detecting code is aparity code or a cyclic code, for example.

The oscillation control section 40 c generates the above-mentionedinformation part and error-detecting code every time a signal block istransmitted, in ascending order of the corresponding division numbers.Based on the generated information and on the latest second information,the oscillation control section 40 c generates a transmissioninformation block TIB to be included in each signal block. FIG. 4Billustrates an example of a transmission information block TIB thusgenerated.

The above-described points are reiterated below using the examples ofFIGS. 4A and 4B. The oscillation control section 40 c generates each IDblock and the corresponding ID block check bits in the order of blocknumbers A, B, . . . , n−1, n. Every time an ID block is generated, theoscillation control section 40 c generates a y+1-bit transmissioninformation block TIB made up of bits P0 to Py together with the secondinformation of c bits that includes the acquired information, the latestwriting pressure information, the latest side switch information, andthe latest charging request information.

FIG. 5 illustrates typical n transmission information blocks TIBgenerated successively as a result of the above-described process. Eachof these n transmission information blocks TIB is associated with one ofthe division numbers (block numbers A, B, . . . , n−1, n). Thetransmission information blocks TIB are generated in the order of thedivision numbers. After completing the generation of the transmissioninformation blocks TIB associated with all division numbers, theoscillation control section 40 c returns to the smallest division numberand repeats the same block generating process.

At the time of signal transmission, the oscillation control section 40 cturns on the output of the oscillator 40 d for a determined time periodto transmit the continuous signal CS for position detection, asillustrated in FIG. 3A. The oscillation control section 40 c thenprovides on-off control of the output of the oscillator 40 d to transmitthe start signal SS. Thereafter, the oscillation control section 40 cprovides on-off control of the output of the oscillator 40 d on thebasis of generated transmission information blocks TIB.

The signal blocks thus transmitted each constitute a signal made up ofthe continuous signal CS, start signal SS, and transmission informationblock TIB, as illustrated in FIG. 3A. The transmission information blockTIB comprises a second modulated signal obtained by modulating thesecond information and by a first modulated signal acquired bymodulating one of a plurality of divided information parts making up thefirst information, as illustrated in FIG. 4B.

As described above, every time a transmission information block TIB isgenerated, the oscillation control section 40 c generates a signalblock. On the basis of the signal blocks thus generated, the oscillationcontrol section 40 c provides on-off control of the output of theoscillator 40 d. As a result of this process, the entire firstinformation is eventually transmitted. The transmission operationperformed by the electronic pen 20 takes place as described above.

Described below in detail with reference to FIGS. 1, 3B and 6 is aseries of example operations performed by the tablet 10 ranging fromdetection of the electronic pen 20 to receipt of the information sentfrom the electronic pen 20.

At a stage where the electronic pen 20 has yet to be detected, themicroprocessor 18 of the tablet 10 repeats the operation of detecting arise in the voltage of each of the electrodes 11X. Specifically, themicroprocessor 18 monitors the digital signal S2 output from theanalog-to-digital converter circuit 17 while causing the selectioncircuit 12 to select all electrodes 11X one by one. When detecting avoltage rise on one electrode 11X as a result of this operation, themicroprocessor 18 proceeds to measure the voltage of each of theelectrodes 11Y. Specifically, the microprocessor 18 monitors the digitalsignal S2 while causing the selection circuit 12 to select allelectrodes 11Y one by one. When detecting a voltage rise on oneelectrode 11Y, the microprocessor 18 determines that the electronic pen20 is approaching the point of intersection between that electrode 11Yand the electrode 11X on which the voltage rise was detected. If voltagerises are detected on a plurality of electrodes 11X or on a plurality ofelectrodes 11Y, the electronic pen 20 may be determined to beapproaching one of the electrodes that bears the highest voltage.

In the example of FIG. 3B, the electrodes 11X are structured to includeelectrodes 11X9 to 11X13 arranged in the Y direction, and the electrodes11Y are structured to include electrodes 11Y18 to 11Y22 arranged in theX direction. It is also illustrated that the electrode 11X on which thevoltage rise was detected in the above process is the electrode 11X11,and that the electrode 11Y on which the voltage rise was detected is theelectrode 11Y20. In the course of the ensuing description, the examplein FIG. 3B will be referred to.

When it is determined that the electronic pen 20 is approaching thepoint of intersection between the electrode 11X11 and the electrode11Y20, the microprocessor 18 causes the selection circuit 12 to selectthe electrode 11X11. In this state, the microprocessor 18, whilemonitoring the digital signal S2, waits for reception of the continuoussignal CS supposed to be sent from the electronic pen 20.

When the electronic pen 20 starts transmitting the continuous signal CS,the voltage of the envelope signal S1 rises, as illustrated in FIG. 3B.As a result, the voltage value represented by the digital signal S2 alsorises. Upon detecting this voltage rise, the microprocessor 18determines whether or not that state continues for a determined time Ts.The determined time Ts is set to be longer than one cycle Td of theabove-mentioned clock signal so that the signal of the transmissioninformation block TIB will not be mistaken for the continuous signal CS.

If it is determined that the voltage rise has continued for thedetermined time Ts, the microprocessor 18 causes the selection circuit12 to select the electrode 11X11 and a plurality of electrodes 11Xnearby (five electrodes 11X9 to 11X13 in the example of FIG. 3B) one byone. From the digital signal S2, the microprocessor 18 acquires thevoltage level of each of the selected electrodes. Of a plurality ofvoltage levels obtained as a result of such measurement, the highestvoltage level is stored into the storage device 19 as a peak voltageVPX. The voltage levels of two adjacent electrodes 11X on both sides ofthe electrode 11X on which the peak voltage VPX was observed are storedinto the storage device 19 as voltages VAX and VBX.

The microprocessor 18 then causes the selection circuit 12 to select theelectrode 11Y20 and a plurality of electrodes 11Y nearby (fiveelectrodes 11Y18 to Y22 in the example of FIG. 3B one by one. From thedigital signal S2, the microprocessor 18 measures the voltage level ofeach of the selected electrodes. Of a plurality of voltage levelsobtained as a result of such measurement, the highest voltage level isstored into the storage device 19 as a peak voltage VPY. The voltagelevels of two adjacent electrodes 11Y on both sides of the electrode 11Yon which the peak voltage VPY was observed are stored into the storagedevice 19 as voltages VAY and VBY.

The microprocessor 18 is configured to perform the above-describedvoltage measuring operation for the duration of the continuous signal CS(e.g., the above-mentioned time period of 2.2 milliseconds). This isintended to suitably receive the start signal SS and the transmissioninformation block TIB following the continuous signal CS. From anopposite point of view, the duration of the continuous signal CS for 2.2milliseconds may be determined as a necessary and sufficient time periodin which the microprocessor 18 completes the above-described voltagemeasuring operation.

The microprocessor 18 calculates the position information on theelectronic pen 20 on the basis of the voltages stored into the storagedevice 19 as described above. For example, the voltages may besubstituted into following mathematical expressions (1) and (2) toobtain coordinates (X, Y) as the position information on the electronicpen 20. In these expressions, P_(X) stands for the X coordinate of theelectrode 11X on which the peak voltage VPX was detected, P_(Y) for theY coordinate of the electrode 11Y on which the peak voltage VPY wasdetected, D_(X) for the pitch at which the electrodes 11X are arranged,and D_(Y) for the pitch at which the electrodes 11Y are arranged.

$\begin{matrix}{\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack} & \; \\{X = {P_{X} + {\frac{D_{X}}{2} \cdot \frac{{VBX} - {VAX}}{{2 \cdot {VPX}} - {VAX} - {VBX}}}}} & (1) \\{X = {P_{Y} + {\frac{D_{Y}}{2} \cdot \frac{{VBY} - {VAY}}{{2 \cdot {VPY}} - {VAY} - {VBY}}}}} & (2)\end{matrix}$

The microprocessor 18 then waits for reception of the start signal SS bymonitoring the digital signal S2, while causing the selection circuit 12to keep selecting the electrode 11X on which the peak voltage VPX wasdetected. When detecting the receipt of the start signal SS, themicroprocessor 18 starts receiving the transmission information blockTIB upon elapse of a determined time Tw from the time t1 at which thestart signal SS was received. The transmission information block TIB isreceived as a sine wave signal modulated using binary ASK as describedabove. The sine wave signal is converted to the digital S2 typically bythe analog-to-digital converter circuit 17 before being supplied to themicroprocessor 18.

Described below in detail with reference to FIG. 6 is an example of theoperation of the microprocessor 18 in connection with the process ofreceiving the transmission information block TIB.

Every time the continuous signal CS for position detection is received,the microprocessor 18 acquires the position information on theelectronic pen 20 as described above, and stores the acquired positioninformation into the storage device 19. Also, every time thetransmission information block TIB including the second information andan information part of the first information is received, themicroprocessor 18 acquires the second information and the informationpart from the block TIB and stores them into the storage device 19.

FIG. 6A schematically illustrates the items of information thusacquired. As illustrated in this figure, the tablet 10 receives aplurality of signal blocks in the order of the above-mentioned divisionnumbers. It should be noted that the signal blocks may or may not bereceived in ascending order of the division numbers starting from thesmallest division number. In the example of FIG. 6A, a block number B isreceived first, followed by block numbers C, . . . , n−1, n, A, B, C, .. . , in that order.

The microprocessor 18 continuously acquires the information parts fromeach of the successively received signal blocks. Upon completion of theacquisition of all information parts constituting the first information,the microprocessor 18 combines the acquired information parts based onthe division numbers to obtain the first information.

Some information parts acquired by the microprocessor 18 may contain abit error that occurred during the transmission. Every time aninformation part is acquired, the microprocessor 18 determines whetheror not that information part is accurate (e.g., whether or not itincludes any bit error) using the error-detecting code included in thesame transmission information block TIB as the information part. If itis determined that the information part is not accurate, themicroprocessor 18 does not use that information part for combinationwith the other information parts and defers executing the combiningprocess until the signal block of the same division number is againreceived, while causing the storage device 19 to hold the secondinformation and the position information. In this manner, themicroprocessor 18 can acquire the first information free of error. FIG.6A illustrates an example in which an error is detected in an ID block(illustrated crossed out) included in the signal block associated withthe division number C received second. In this case, the microprocessor18 waits for the signal block associated with the division number C tobe again received, before combining the received information parts toacquire the first information.

Upon completion of the acquisition of the first information, themicroprocessor 18 associates a plurality of pieces of positioninformation and a plurality of pieces of second information held so farin the storage device 19 with the acquired first information. As needed,the microprocessor 18 associates each of the pieces of positioninformation and each of the pieces of second information with theacquired first information before outputting them to the computer 30.This enables the microprocessor 18 and the computer 30 to process boththe position information and the second information received up to thecompletion of the acquisition of the first information as theinformation associated with the first information.

Under the above scheme, the computer 30 cannot acquire the positioninformation and the second information until the tablet 10 completes theacquisition of the first information. This can cause the user toexperience delays in the processing of the computer 30, such as delayeddisplay of the locus of the electronic pen 20. To bypass thisphenomenon, the tablet 10 may output at least some information parts tothe computer 30 without waiting for completion of the acquisition of thefirst information.

As a specific example, the microprocessor 18 may have a function ofstoring one or more first information parts acquired in the past. Untilacquisition of the entire first information is completed, every time anew signal block is received, the microprocessor 18 may estimate thecurrently received first information part on the basis of the divisionnumbers and ID blocks included in the signal blocks received so far andthe first information stored in the past. Even before acquisition of thefirst information as a whole is completed, the microprocessor 18 mayassociate the successively received position information and secondinformation with the estimated first information and output the combinedinformation successively to the computer 30.

For example, it may happen that the electronic pen 20 enters adetectable area of the tablet sensor 11 but immediately leaves it sothat acquisition of the first information is incomplete. In that case,the example function above enables the computer 30 to process theposition information, writing pressure information, and otherinformation by use of the estimated first information. This makes itpossible to display the locus of the electronic pen 20 even if the firstinformation (unique ID) cannot be recognized due to excessively rapid“in-and-out movements” of the electronic pen 20.

As a more specific example, suppose that, of the transmissioninformation blocks TIB illustrated in FIG. 6A, only two transmissioninformation blocks TIB associated with the division numbers A and B areacquired as a result of rapid “in-and-out movements” of the electronicpen 20. In this case, if the microprocessor 18 has acquired and storedthe associated first information in the past, the microprocessor 18 maycompare the ID blocks included in the two transmission informationblocks TIB with the stored first information (unique ID). This allowsthe microprocessor 18 to estimate the entire first information includingthe ID blocks associated with the division numbers C to n. That in turnenables the computer 30 to process the position information, writingpressure information, and other information acquired from the twotransmission information blocks TIB as the information on the electronicpen 20 having the estimated first information.

As described above, the input system 1 of this embodiment divides thefirst information, which is too large to be transmitted in onetransmission information block TIB, into a plurality of signal blockseach including the continuous signal CS for position detection beforetransmitting the signal blocks. This makes it possible for theelectronic pen 20 to transmit large-size information to the tablet 10without reducing the sampling rate of the position information.

Because the division number is assigned to each signal block, the tablet10 can correctly restore the first information on the basis of thedivision numbers. Since the error-detecting code is attached to eachsignal block, it is also possible to prevent the restoration of thefirst information based on an erroneous information part.

The tablet 10 retains in the storage device 19 the received secondinformation as well as the position information obtained beforeacquisition of the first information is completed. It follows that uponcompletion of the acquisition of the first information, the tablet 10can make effective use of such retained information as the informationassociated with the first information.

Although example embodiments have been described above, this is notlimitative. It is evident that embodiments can be implemented in diverseforms within the scope and spirit thereof.

For example, although the input system 1 explained in conjunction withthe above embodiments is configured to perform position detection andcommunication by use of a self-capacitance type touch-sensitive panel,embodiments can also be adapted advantageously to other types ofsystems. For example, embodiments may be adapted to a mutual capacitancetype touch panel or to an input system that performs position detectionand communication using the electromagnetic induction scheme.

FIG. 7 illustrates a structure of an electronic pen 20 a for use with aninput system that performs position detection and communication usingthe electromagnetic induction scheme. As illustrated in the figure, theelectronic pen 20 a is configured to have a controller 60, a powersupply circuit 61, and a resonant circuit 62. The resonant circuit 62 ismade up of a coil 63, a capacitor 64, and a variable capacitancecapacitor 65. The capacitor 64 and the variable capacitance capacitor 65are connected in parallel to the coil 63. A capacitor 66 is furtherconnected to the resonant circuit 62 via a switch 67.

The resonant circuit 62 is configured to resonate with electromagneticwaves of a determined frequency transmitted from a position detectingdevice (tablet). The controller 60 is configured to transmit a signalusing induced power generated by resonance. That signal may bestructured in the same manner as the signal blocks used by theabove-described embodiment. Thus the input system that performs positiondetection and communication using the electromagnetic induction schememay, as with the input system 1 of the above-described embodiment,transmit large-size information from the position indicator to theposition detecting device without reducing the sampling rate of theposition information.

Although it was explained that the above embodiment transmits both thefirst and the second information in each signal block, it is notmandatory to transmit the second information. Embodiments may thus beadapted advantageously to electronic pens that do not transmit thesecond information.

It was also explained in conjunction with the above embodiment that thetransmission information blocks TIB are sent as an intermittent signalincluding, at intervals of a determined time period (specifically oneclock cycle), a time period during which each transmission informationblock TIB is at the low level and that the continuous signal CS remainsat the high level over a period longer than the determined time period.Alternatively, the transmission information blocks TIB may be sent as anintermittent signal including a time period during which eachtransmission information block TIB is at the high level, with thecontinuous signal CS remaining at the low level over a time periodlonger than the determined time period.

It was further explained in conjunction with the above embodiment thatas illustrated in FIG. 3A, the entire continuous signal CS for use indetecting the position of the position indicator is transmitted in onepass. Alternatively, the continuous signal CS may be transmitted in aplurality of divided parts.

DESCRIPTION OF REFERENCE SYMBOLS

1 Input system

10 Tablet

11 Tablet sensor

11X, 11Y Electrode

12 Selection circuit

13 Amplifier circuit

14 Band-pass filter

15 Detector circuit

16 Sample hold circuit

17 Analog-to-digital converter circuit

18 Microprocessor

19 Storage device

20 Electronic pen

30 Computer

40 Controller

40 a Unique ID storage section

40 b Information acquisition section

40 c Oscillation control section

40 d Oscillator

41 Voltage converter circuit

42 Diode

43 to 46, 64 to 66 Capacitor

47 Resistive element

48, 49, 67 Switch

50 Vibrator

51 Conductor core

52 Tip conductor

53 Charging terminal

60 Controller

61 Power supply circuit

62 Resonant circuit

63 Coil

CS Continuous signal

P1 to P6 Control terminal

S1 Envelope signal

S2 Digital signal

TIB Transmission information block

SS Start signal

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A signal transmission method, comprising:dividing, by a position indicator, first information, which is a digitalsignal of a first defined number of bits, into a plurality ofinformation parts as digital signals of a second defined number of bitssmaller than the first defined number of bits; and transmitting, fromthe position indicator to a position detecting device, the informationparts, and distinguishing information usable for distinguishing theinformation parts from each other, wherein each of the information partsis transmitted with second information different from the firstinformation.
 2. The signal transmission method according to claim 1,wherein the distinguishing information is usable for reconstructing thefirst information.
 3. The signal transmission method according to claim1, comprising transmitting, from the position indicator to the positiondetecting device, an error detection code usable for detection of anerror in the information parts.
 4. The signal transmission methodaccording to claim 1, wherein the first information is informationunique to the position indicator.
 5. The signal transmission methodaccording to claim 4, wherein the information unique to the positionindicator is at least one of ID information that identifies the positionindicator, user ID information assigned to the position indicator, ormanufacturer information of the position indicator.
 6. The signaltransmission method according to claim 1, wherein the second informationis pressure information detected by the position indicator.
 7. Thesignal transmission method according to claim 6, wherein the pressureinformation is pen tip pressure information of the position indicator.8. A signal transmission method, comprising: dividing, by a positionindicator, first information, which is a digital signal of a firstdefined number of bits, into a plurality of information parts as digitalsignals of a second defined number of bits smaller than the firstdefined number of bits; and transmitting, from the position indicator toa position detecting device, the information parts, and distinguishinginformation usable for distinguishing the information parts from eachother.
 9. The signal transmission method according to claim 8, whereinthe distinguishing information is usable for reconstructing the firstinformation.
 10. The signal transmission method according to claim 8,comprising transmitting, from the position indicator to the positiondetecting device, an error detection code usable for detection of anerror in the information parts.
 11. The signal transmission methodaccording to claim 8, wherein the first information is informationunique to the position indicator.
 12. The signal transmission methodaccording to claim 11, wherein the information unique to the positionindicator is at least one of ID information that identifies the positionindicator, user ID information assigned to the position indicator, ormanufacturer information of the position indicator.
 13. The signaltransmission method according to claim 8, comprising transmitting, fromthe position indicator to the position detecting device, secondinformation different from the first information with each of theinformation parts, wherein the second information is pressureinformation detected by the position indicator.
 14. The signaltransmission method according to claim 13, wherein the pressureinformation is pen tip pressure information of the position indicator.15. A signal transmission method, comprising: dividing, by a positionindicator, first information, which is a digital signal of a firstdefined number of bits, into a plurality of information parts as digitalsignals of a second defined number of bits smaller than the firstdefined number of bits; and transmitting, from the position indicator toa position detecting device, the information parts, and an errordetection code usable for detection of an error in the informationparts.
 16. The signal transmission method according to claim 15,comprising transmitting, from the position indicator to the positiondetecting device, distinguishing information usable for distinguishingthe information parts from each other and usable for reconstructing thefirst information.
 17. The signal transmission method according to claim15, comprising transmitting, from the position indicator to the positiondetecting device, second information different from the firstinformation with each of the information parts.
 18. The signaltransmission method according to claim 15, wherein the first informationis information unique to the position indicator.
 19. The signaltransmission method according to claim 18, wherein the informationunique to the position indicator is at least one of ID information thatidentifies the position indicator, user ID information assigned to theposition indicator, or manufacturer information of the positionindicator.
 20. The signal transmission method according to claim 15,comprising transmitting, from the position indicator to the positiondetecting device, second information different from the firstinformation with each of the information parts, wherein the secondinformation is pressure information detected by the position indicator.21. The signal transmission method according to claim 20, wherein thepressure information is pen tip pressure information of the positionindicator.